Legal Question in Family Law in Maryland

You can file a petition to change custody, but the mere fact your ex isn't working doesn't disqualify her from having custodial status. As to your current joint status, it's unusual for parents to have joint physical status when they aren't living near one another, because of the obvious impracticality and hardship on the child. Your ex does have a duty of support, and if there were an effort to change the amount of your child support payment, you could charge her with "voluntary impoverishment" and ask the court to impute income to her for the purpose of calculating your respective child support obligations, based on her work history and job skills.